68'-70' rear frame rail variances?

[68RT440]

Hey guys, I have a question. Im replacing the rear frame rails in my 68 and I scored a set of m int 68-70 B body rails from out west. I have the rear of the car jigged with square tubing and took a ton of measurments as well as I have a frame dimension sheet. I took only one rail out, and Ive noticed that the rail that I have is just slightly different in areas than the ones that are in my car. Overall they are nearly identical, but Im getting a few measurments that are an 1/8" off here, and 1/16" off there. After laying the rails side by side, Ive noticed that there are a couple differences between the rails. Im just wondering if there were a couple different plants stamping rails between 68-70 or if they mabye changed the tooling after a while. Im sure they are the correct rails, but the slight difference has me wondering..thanks

[green69rt]

Hey guys, I have a question. Im replacing the rear frame rails in my 68 and I scored a set of m int 68-70 B body rails from out west. I have the rear of the car jigged with square tubing and took a ton of measurments as well as I have a frame dimension sheet. I took only one rail out, and Ive noticed that the rail that I have is just slightly different in areas than the ones that are in my car. Overall they are nearly identical, but Im getting a few measurments that are an 1/8" off here, and 1/16" off there. After laying the rails side by side, Ive noticed that there are a couple differences between the rails. Im just wondering if there were a couple different plants stamping rails between 68-70 or if they mabye changed the tooling after a while. Im sure they are the correct rails, but the slight difference has me wondering..thanks

I've been going thru my 69 and found the same as you, lots of little differences in parts on the car vs what I've bought (mostly from AMD.)  SO I checked my field service manual for the chassis alignment dimensions.  They say all are to plus or minus 1/4 inch!!!  Seems like a lot of slop but I guess there were looser tollerances back then.  I've tightened up the measurements where I can and ignored the rest.  So bend, hammer and cut to satisfy yourself then don't look back.

[68RT440]

Awesome, thanks for the reply. that makes me feel a lot better 

[Kern Dog]

Seems a little scary, but it sure explains a few things!
Ever see a car "crab walk" down the road ? Many times it is due to the axle being out of square with the car.  I've seen several cars with more tire clearance on one side. My Charger is one of them. If you run on narrow tires, you can't tell. Try to fit in the widest tires and you may find that each corner of the car has its own unique measurement!

[green69rt]

Agree, my idea on this frame alignment thing is try to get it as close as you can, or take it to a frame shop and put it on their jig for straightening but doen't rely on the measurements of individual pieces.  Also many of our old cars have been hit so parts may be bent so little or curved so gently that comparing measurements between new and old parts may yield differences.  Rely more on the total frame dimensions from the field service manual.  Also take a little time to just "eyeball" the straightness of the car, sometimes you can see something that warrents more measurement.

A hint on the rear frame rails.  When replacing mine I found a good way to tell if you're good is to tack or screw everything together including the rear valance and valance corners.  Also install the rear leaf springs.   When everything fits nicely then you know you're pretty close.

[Brock Lee]

Yeah, there was a huge tolerance gap back then. This is why most all parts have ovaled holes for final alignment before tightening down.

[MoparManJim]

I'm glad I found this thread, I'm tackling this very subject myself. I know how you all feel on getting it just right or very close to correct.